Infection associated with implantation of medical devices is a serious health and economic concern. Today, infections associated with implanted medical devices are not very common due to care and precautions taken during surgical implantation of the devices. However, when infection associated with an implanted medical device (IMD) does occur, explanting the device is often the only appropriate course of action.
For IMDs having a powered component, such as implantable cardiac pacemakers, cardioverter/defibrillators having pacing capabilities, other electrical stimulators including spinal cord, deep brain, nerve, and muscle stimulators, infusion devices, cardiac and other physiologic sensors, cochlear implants, etc., the powered component is typically enclosed in a housing that is implanted subcutaneously at a surgically prepared site, referred to as a “pocket”. Associated devices, such as elongated medical electrical leads or drug delivery catheters, extend from the pocket to other subcutaneous sites or deeper into the body to organs or other implantation sites.
Surgical preparation and implantation are conducted in a sterile field, and the IMD components are packaged in sterile containers or sterilized prior to introduction into the sterile field. However, despite these precautions, there always is a risk of introduction of microbes into the pocket. Surgeons therefore typically apply disinfectant or antiseptic agents to the skin at the surgical site prior to surgery, directly to the site before the incision is closed, and prescribe oral antibiotics for the patient to ingest during recovery.
Despite these precautions, infections do occur. In addition, once the pocket becomes infected, the infection can migrate along the lead or catheter to the heart, brain, spinal canal or other location in which the lead or catheter is implanted. Such a migrating infection can become intractable and life-threatening, requiring removal of the IMD in the pocket and associated devices, such as leads and catheters. Removal of a chronically implanted lead or catheter can be difficult and dangerous. Accordingly, aggressive systemic drug treatment is prescribed to treat such infections. However, early detection of infection associated with implanted medical devices may allow for earlier intervention, resulting in fewer device explants.
One approach for preventing such infections is to dispose an anti-infective covering, coating, pouch, or the like about the device prior to implantation. The coating includes an anti-infective agent, such as silver particles or an antibiotic, which can elute from the coating to prevent infection in the subcutaneous pocket in which the device is implanted. While effective in many circumstances, some drawbacks still remain.
For example, for devices in which the device housing serves as a return electrode, such as unipolar pacemakers, defibrillators, neurostimulators and the like, placing a coating or covering about the device inhibits or abolishes conductance of the housing and renders the device and therapy ineffective. Some agents that are conductive, such as silver particles, can be coated directly on such devices. However, the ability to control release rate is diminished relative to polymeric systems. In addition, silver particles directly coated onto a device may suffer from reduced antimicrobial activity due to sterilization and tend to flake off the device.